Inter-MeNB handover method and device in a small cell system

ABSTRACT

An embodiment of the present disclosure may provide an inter-MeNB handover method in a small cell system, including: making, by a source MeNB and/or target MeNB, a determination as to whether to maintain a SeNB when handover is performed; and triggering different handover processes according to a result of the determination as to whether to maintain the SeNB. Another embodiment of the present disclosure may further provide an inter-MeNB handover device in a small cell system. With the inter-MeNB handover method and device in a small cell system provided by the present disclosure, unnecessary deletion and re-establishment of the bearers at the SeNB for the UE may be reduced. False bearer deletion may be avoided and data forwarding may be reduced. Furthermore, the SeNB may be maintained according to network deployment and SGW re-selection may be supported. Therefore, system capacity and transmission speed of the data may be improved.

PRIORITY

This application is a National Phase Entry of PCT InternationalApplication No. PCT/KR2015/007197, which was filed on Jul. 10, 2015, andclaims a priority to Chinese Patent Application No. 201410328143.5,which was filed on Jul. 10, 2014, and claims a priority to ChinesePatent Application No. 201510136863.6, which was filed on Mar. 26, 2015,the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a wireless communication technology,and more particularly, to an inter-Master enhanced Node B (MeNB)handover method and device in a small cell System.

BACKGROUND ART

Modern mobile communication tends to provide users with multimediaservices transmitted at a high speed. FIG. 1 is a schematic diagramillustrating architecture of a System Architecture Evolution (SAE).

A User Equipment (UE) 101 is a terminal device for receiving data. AnEvolved Universal Mobile Telecommunications System (UMTS) TerrestrialRadio Access Network (E-UTRAN) 102 is a Radio Access Network (RAN). TheRAN includes a macro eNodeB/NodeB. The macro eNodeB/NodeB provides theUE with a radio network interface, with which the UE may access theradio network. A Mobile Management Entity (MME) 103 is responsible formanaging a mobile context, session context and security information ofthe UE. A Serving GateWay (SGW) 104 mainly provides a function of a userplane. The MME 103 and SGW 104 may be located at a same physical entity.A Packet Data Network Gateway (PGW) 105 is responsible for charging andlawful interception, etc. The PGW 105 and SGW 104 may be located at asame physical entity. A Policy and Charging Rule Function (PCRF) 106provides Quality of Service (QoS) policies and charging rules. A ServingGeneral Packet Radio Service (GPRS) Support Node (SGSN) 108 is a networknode device, which provides data transmission with routing in aUniversal Mobile Telecommunications System (UMTS). A Home SubscriberServer (HSS) 109 is a home sub-system of the UE and is responsible forprotecting user information. The user information includes a currentposition of the UE, an address of a serving node, user securityinformation and packet data context of the UE, etc.

The Generation Partnership Project (3GPP) proposes a requirement ofsmall cell enhancement in Rel-12. A target scenario of the small cellenhancement includes: a scenario covered by a macro cell, a scenario,which is not covered by the macro cell, indoor and outdoor enhancement,ideal and non-ideal return enhancement, as shown in FIG. 2.

In the scenario covered by the macro cell, a technology for usinginter-eNB carrier aggregation is proposed. The macro cell and small cellmay work at different bands. There may be two kinds of architecture ofthe technology for using the inter-eNB carrier aggregation. In the firstkind of architecture, user plane data is separated with a Radio AccessNetwork (RAN). In the second kind of architecture, the user plane datais separated with a Core Network (CN). In the architecture, in which theuser plane data is separated with the CN, as for a bearer established ina Pico cell, the data is directly sent to the Pico cell via the SGW inthe CN and the user plane data is not forwarded via the macro cell.

In the architecture of the small cell, the UE may simultaneously receiveor transmit data on two eNBs, which is called dual-connectivity. In thetwo eNBs, only one eNB is responsible for transmitting a Radio ResourceControl (RRC) message to the UE and responsible for interacting with acontrol plane entity of the CN which is MME. The above eNB is called aMeNB and the other eNB is called a Secondary eNB (SeNB). A cell of theUE on the MeNB is a Primary cell (Pcell) of the UE. A Radio ResourceControl (RRC) message is sent to the UE via the Pcell and the othercells are Secondary cells (Scell)s. A Scell of the UE in the SeNB is apScell. The pScell has an Uplink (UL) physical layer control channel andthe other Scells do not have the UL physical layer control channel Acell group in the MeNB is a Master Cell Group (MCG) and a cell group atthe SeNB is a Secondary Cell Group (SCG). Resources of the SCG at the UEside are configured by the SeNB and the SeNB sends configurations of theUE to the MeNB via an RRC container, The MeNB sends the configurationsof the UE to the UE. The MeNB does not parse the RRC container or theMeNB parses the RRC container but does not change the configurations ofthe RRC container.

DISCLOSURE Technical Problem

With movement of the UE or change of channel quality, when the MeNBdetermines to handover a UE from the MeNB to a new eNB, the new eNB maybe called a target MeNB and inter-MeNB handover may occur. In thehandover process of the MeNB, all bearers (including bearers at thesource MeNB and bearers at the SeNB) are handed over to the target MeNB.The drawbacks of this method are that the bearers are frequentlyre-configured and the dual-connectivity is not effectively utilized toincrease system capacity and improve the data transmission speedprovided to the UE.

In the present disclosure, following aspects are addressed: how to makea determination as to whether to maintain the SeNB; how to obtain whichbearer is configured at the SeNB by the target MeNB; how to correctlyconfigure resource for the bearer of the UE by the source MeNB andtarget MeNB; how to notify the SeNB by the target MeNB which UE ishanded over; how to correctly notify the CN of information of bearerswitch by the target MeNB to avoid that the MME may falsely release somebearers; and how to support SGW relocation in an inter-MeNB handoverprocess.

Technical Solution

Embodiments of the present disclosure provide an inter-MeNB handovermethod and device in a small cell system, to enhance system capacity andtransmission speed of the data.

An embodiment of the present disclosure provides an inter-MeNB handovermethod in a small cell system, including: determining, by a source MeNB,as to whether to maintain a secondary eNB (SeNB) when a handover isperformed; and triggering a handover process based on a result of thedetermination as to whether to maintain the SeNB.

Another embodiment of the present disclosure provides an inter-masterenhanced NodeB (MeNB) handover method in a small cell system,comprising: determining, by a target MeNB, as to whether to maintain asecondary eNB (SeNB) when a handover is performed; and triggering ahandover process based on a result of the determination as to whether tomaintain the SeNB.

Another embodiment of the present disclosure provides an inter-masterenhanced NodeB (MeNB) handover device in a small cell system, the devicecomprising: a determination module configured to make a determination asto whether to maintain a secondary eNB (SeNB) when a handover isperformed; and a handover module configured to trigger a differenthandover process according to a result of the determination as towhether to maintain the SeNB.

Another embodiment of the present disclosure provides an inter-MeNBhandover method in a small cell system, including: making, by a sourceMeNB and/or target MeNB, a determination as to whether to maintain aSecondary enhanced NodeB (SeNB) when handover is performed; andtriggering different handover processes according to a result of thedetermination as to whether to maintain the SeNB.

Preferably, the method for making, by the source MeNB and/or targetMeNB, the determination as to whether to maintain the SeNB includes:making, by the source MeNB, the determination as to whether to maintainthe SeNB; sending, by the source MeNB, a handover request message to thetarget MeNB if the result of the determination made by the source MeNBis maintaining the SeNB; receiving, by the source MeNB, a handoverrequest acknowledgement message from the target MeNB. The handoverrequest acknowledgement message includes the result of the determinationas to whether to maintain the SeNB.

Preferably, the method for making, by the source MeNB and/or targetMeNB, the determination as to whether to maintain the SeNB includes:sending, by the source MeNB, a handover request message to the targetMeNB; receiving, by the source MeNB, a handover request acknowledgementmessage from the target MeNB.

The handover request acknowledgement message includes: the result of thedetermination as to whether to maintain the SeNB.

Preferably, the method for making, by the source MeNB and/or targetMeNB, the determination as to whether to maintain the SeNB includes:making, by the source MeNB, the determination as to whether to maintainthe SeNB and obtaining the result of the determination as to whether tomaintain the SeNB.

Preferably, the method for making, by the source MeNB and/or targetMeNB, the determination as to whether to maintain the SeNB includes:sending, by the source MeNB, a handover request message to the targetMeNB; receiving, by the source MeNB, a handover request acknowledgementmessage from the target MeNB; the handover request acknowledgementmessage including: information indicating whether there is an X2interface between the target MeNB and the SeNB or information indicatingwhether it is feasible to maintain the SeNB; making, by the source MeNB,the determination as to whether to maintain the SeNB according to theinformation in the handover request acknowledgement message at the SeNB.

Preferably, the handover request message includes one of or combinationof multiple kinds of the following information: a cell Identity (ID) ofa Secondary cell (Scell) of the UE at the SeNB and/or an eNB ID of theSeNB; bearers of the UE at the SeNB; whether the bearer of the UE at theSeNB are split bearer or SeNB Cell Group (SCG) bearers; a measurementresult of the UE; an ID of the UE at the SeNB; and a Downlink (DL)Tunnel Endpoint Identifier (TEID) and DL transmission layer address ofan X2 interface allocated by the SeNB to the split bearer.

Preferably, the method for triggering the different handover processesaccording to the result of the determination as to whether to maintainthe SeNB includes: switching bearers from the SeNB to the target MeNB ina first handover process if the result of the determination is notmaintaining the SeNB; and maintaining the bearers at the SeNB in asecond handover process if the result of the determination ismaintaining the SeNB.

Preferably, the method for maintaining the bearers at the SeNB includes:allocating, by the target MeNB, a DL TEID and DL transmission layeraddress of an interface between the target MeNB and a Serving GateWay(SGW) to split bearer at the SeNB, sending, by the target MeNB, the DLTEID and DL transmission layer address to the source MeNB via a handoverrequest acknowledgement message, and sending, by the source MeNB, the DLTEID and DL transmission layer address to the Mobile Management Entity(MME) via a path switch request message; as for SCG bearer at the SeNB,not allocating, by the target MeNB, the DL TEID and DL transmissionlayer address to the SCG bearers and sending an Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) Radio Access Bearer (E-RAB)modification indication or enhanced path switch request message to theMME; the E-RAB modification indication or enhanced path switch requestmessage including: a Tracking Area Identity and/or E-UTRAN Cell GlobalIdentifier (ECGI) of a Primary cell (Pcell) of the target MeNB, and aTAI and/or ECGI of a S cell at the SeNB; and as for bearer, which ishanded over to the target MeNB and in case of data forwarding is needed,allocating, by the target MeNB, a TEID and transmission layer address ofan X2 interface for the data forwarding.

A Radio Resource Control (RRC) re-configuration message sent from thesource MeNB to the UE does not include information instructing the UE todelete a SCG.

Preferably, when the result of the determination is maintaining theSeNB, the method further includes: making, by the target MeNB, adetermination as to whether to modify configuration of bearer of the UEat the SeNB according to the configuration of the bearer of the UE madeby the target MeNB and/or UE capability information, sending, by thetarget MeNB, an SCG configuration request message to the SeNB if aresult of the determination at the SeNB is modifying the configurationof the bearer of the UE at the SeNB and sending, by the SeNB, an SCGconfiguration response message to the target MeNB. Preferably, the SCGconfiguration request message includes: an ID of the UE at the SeNB, aMeNB UE X2AP ID allocated by the target MeNB for the UE, which is usedto identify the UE between the target MeNB and the SeNB, and/or a newkey of the UE in a Scell calculated by the target MeNB. The SCGconfiguration response message includes: a RRC container configured bythe SeNB and a SeNB UE X2AP ID, which is allocated by the SeNB toidentify the UE between the target MeNB and the SeNB.

Preferably, when the result of the determination is maintaining theSeNB, the method further includes: sending, by the target MeNB, a UEconfiguration completion message to the SeNB. The UE configurationcompletion message includes: a MeNB UE X2AP ID between the target MeNBand the SeNB allocated by the target MeNB for the UE. If the target MeNBmodified configuration of the SeNB before the target MeNB sends the UEconfiguration completion message to the SeNB, the UE configurationcompletion message includes: a SeNB UE X2AP ID, which is allocated bythe SeNB to identify the UE between the target MeNB and the SeNB. If thetarget MeNB didn't modify the configuration of the SeNB before thetarget MeNB sends the UE configuration completion message to the SeNB,the UE configuration completion message comprises information, which isused by the SeNB to identify the UE. The information, which is used bythe SeNB to identify the UE is a cell ID of a S cell at the SeNB and aCell Radio Network Temporary Identifier (C-RNTI) of the UE in the Scell.If there are the SeNB multiple serving Scells at the SeNB, theinformation, which is used by the SeNB to identify the UE includes:multiple Pairs of cell ID of the Scell and C-RNTI; or the information,which is used by the SeNB to identify the UE is the SeNB UE X2AP ID ofthe UE allocated by the SeNB. When the information, which is used by theSeNB to identify the UE is the SeNB UE X2AP ID of the UE allocated bythe SeNB, the UE configuration completion message further includes: theID of the source MeNB and/or the MeNB UE X2AP ID allocated by the sourceMeNB.

Preferably, as for split bearer, the UE configuration completion messagefurther includes: an E-RAB ID and a TEID and transmission layer addressallocated by the target MeNB.

In a situation that an SGW is re-selected, as for SCG bearer, the UEconfiguration completion message further includes: a UL TEID and ULtransmission layer address allocated by a new SGW.

Another embodiment of the present disclosure further provides aninter-MeNB handover device in a small cell system, including: adetermination module and a handover module.

The determination module is to make a determination as to whether tomaintain a Secondary enhanced NodeB (SeNB) when handover is performed;and

the handover module is to trigger different handover processes accordingto a result of the determination as to whether to maintain the SeNB.

Advantageous Effects

It may be seen from the above technical scheme that with the inter-MeNBhandover method and device in a small cell system, unnecessary deletionand re-establishment of the bearer of the UE at the SeNB may be reduced.False bearer deletion may be avoided and data forwarding may be reduced.Furthermore, whether to handover the SeNB or maintain the SeNB may bedetermined according to network deployment and SGW relocation may besupported. Therefore, system capacity and transmission speed of the datamay be improved.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating architecture of aconventional SAE system;

FIG. 2 is a schematic diagram illustrating an enhanced deploymentscenario of the small cell;

FIG. 3 is a schematic diagram illustrating inter-MeNB handover methodone in a small cell system;

FIG. 4 is a schematic diagram illustrating inter-MeNB handover methodtwo in a small cell system;

FIG. 5 is a schematic diagram illustrating inter-MeNB handover methodthree in a small cell system;

FIG. 6 is a schematic diagram illustrating inter-MeNB handover methodfour in a small cell system;

FIG. 7 is a signaling flow in accordance with an embodiment of thepresent disclosure;

FIG. 8 is a signaling flow chart in accordance with an embodiment of thepresent disclosure;

FIG. 9 is a signaling flow chart in accordance with an embodiment of thepresent disclosure; and

FIG. 10 is a schematic diagram illustrating structure of a preferredinter-MeNB handover device in a small cell system in accordance with anexample of the present disclosure.

MODE FOR INVENTION

To make the objective, technical solution and the merits of the presentdisclosure more apparent, the present disclosure may be described indetail with reference to accompanying figures.

FIG. 3 may be a schematic diagram illustrating inter-MeNB handovermethod one in a small cell system. The main process of the method mayinclude: making, by a source MeNB, a determination as to whether tomaintain a SeNB and triggering different processes according to a resultof the determination. If the result of the determination of the sourceMeNB is keeping the SeNB unchanged, a target MeNB may further make adetermination as to whether to maintain the SeNB and notify the sourceMeNB of the result of the determination. The source MeNB may send acorresponding message to the UE. After receiving an RRC re-configurationresponse message from the UE, the target MeNB may send a correspondingmessage to the CN, so that bearer of the UE at the SeNB is kept in bothUE and CN side. In the above process, both the source MeNB and targetMeNB may make a determination as to whether to keep the SeNB. In orderto distinguish the determinations made by the source MeNB and the targetMeNB, the determination made by the source MeNB may be called an initialdetermination and the determination made by the target MeNB may becalled a final determination. Specifically, the method shown in FIG. 3may include following blocks.

At step 301, the source MeNB may determine to hand over the UE to thetarget MeNB.

At step 302, the source MeNB may make the initial determination as towhether to change the SeNB. If the source MeNB determines to hand overthe bearers at the SeNB to the target MeNB, block 307 may be executed.If the source MeNB determines to keep the SeNB unchanged, block 303 maybe performed.

At this step, the source MeNB may make the determination as to whetherto keep the SeNB unchanged according to a UE's measurement report. Forinstance, if the UE's measurement report shows that signal quality ofthe UE in a Scell of the SeNB is good enough, the source MeNB maydetermine that the SeNB may be kept unchanged. If the UE's measurementreport shows that the signal quality of the UE in the Scell of the SeNBis not good enough, the source MeNB may determine to hand over thebearers at the SeNB.

At step 303, the source MeNB may send a handover request message to thetarget MeNB.

The handover request message includes contents in the existing 3GPPspecification TS36.423. For instance, the contents may include ato-be-established Evolved Radio Access Bearer (E-RAB) list, the UE'smeasurement report and UE capability information, etc. Each item ofto-be-established E-RAB information may include: an E-RAB Identity (ID),E-RAB QoS information and UL GPRS Tunnelling Protocol (GTP) tunnelendpoint identity (TEID).

The handover request message may further include one kind of thefollowing information or combination of multiple kinds of the followinginformation:

-   -   a cell ID of the S cell of the UE at the SeNB and/or an eNB ID        of the SeNB.    -   bearer of the UE at the SeNB. That is, which bearer of the UE is        at the SeNB. Specifically, it may be denoted with different        E-RAB lists. For instance, an E-RAB list which may be handed        over to the target MeNB and an E-RAB list at the SeNB. In an        alternative, the to-be-established E-RAB list may include all        E-RAB information of the UE. An information element cell id of        the Scell or an indication that the bearer is at the SeNB may be        added to the to-be-established E-RAB information. The bearer        information at the SeNB may include the new information element,        while the E-RAB information, which is to be handed over to the        target MeNB, may not include the new information element. The        target MeNB may obtain which bearer of the UE is at the SeNB        with the above two methods. As for split bearers, since a bearer        may not only consume resources at the MeNB, but also consume        resources at the SeNB, the latter method may have significant        advantages:    -   whether the bearer of the UE at the SeNB is split bearer or        secondary cell group (SCG) bearer. The target MeNB may obtain        whether the bearer at the SeNB is the split bearer or SCG bearer        with the new information element.    -   the UE's measurement report;    -   the ID of the UE at the SeNB. The ID of the UE at the SeNB may        be the cell ID of the Scell of the UE at the SeNB and Cell Radio        Network Temporary Identifier (C-RNTI) of the UE in the Scell.        The ID of the UE at the SeNB may be an X2 Application Protocol        (X2 AP) ID of the UE over an interface between the source MeNB        and the SeNB which includes an SeNB UE X2 AP ID allocated by the        SeNB, and/or an MeNB UE X2AP ID allocated by the source MeNB        and/or an ID of the source MeNB.    -   a DL Tunnel Endpoint Identifier (TEID) and a DL transmission        layer address of an X2 interface allocated by the SeNB to the        split bearer.

At step 304, the target MeNB may make a determination as to whether tochange the SeNB.

At this step, the target MeNB may make a determination as to whether tochange the SeNB according to the UE's measurement report, ID of the SeNBor ID of the Scell at the SeNB received from the source MeNB. Forinstance, the target MeNB may make a determination as to whether thereis an X2 interface between the target MeNB and the SeNB according to theeNB ID of the SeNB or the cell ID of the Scell at the SeNB. If there isan X2 interface and the UE's measurement report received from the MeNBshows that e.g the signal of the Scell at the SeNB is good enough, thetarget MeNB may determine to keep the SeNB unchanged. If there is no X2interface between the target MeNB and SeNB or the UE's measurementreport received from the MeNB shows that e.g. the signal of the Scell atthe SeNB is not good enough, the target MeNB may determine not tomaintain the SeNB. The target MeNB may take account of other factors(such as O&M configuration) without affecting the main contents of thepresent disclosure.

If the SeNB is not changed, bearer originally established at the SeNBmay not be handed over to the target MeNB and still kept at the SeNB.Therefore, frequent bearer deletion and bearer establishment processesmay not be needed. After the handover of the MeNB, the dual-connectivitymay continue to be used, which may enhance speed for transmitting datato the UE.

When the bearer at the SeNB is maintained and not handed over, thetarget MeNB may determine to modify the configuration of the bearer ofthe UE at the SeNB according to the configuration of the UE made by thetarget MeNB and/or UE capability information and/or other information,etc. If the target MeNB determines to modify the configuration of thebearer at the SeNB, the target MeNB may send an SCG configurationrequest message to the SeNB. The target MeNB may obtain the SeNB of theUE according to the cell ID of the Scell of the UE at the SeNB and/orthe ID of the SeNB in the handover request message in block 303. The SCGconfiguration request message may include the ID of the UE at the SeNB.The ID of the UE at the SeNB is the same as that in block 303, withoutgoing into the details. The SCG configuration request message mayfurther include the MeNB UE X2AP ID allocated by the target MeNB for theUE. The MeNB UE X2AP ID is used to identify the UE between the targetMeNB and SeNB. The SCG configuration request message may be the existingSeNB modification request message or a new message. The SCGconfiguration request message may further include a new key of the UE inthe Scell calculated by the target MeNB. The SeNB may send an SCGconfiguration response message to the target MeNB. The SCG configurationresponse message may include a Radio Resource Control (RRC) containercontaining the updated air interface configuration by the SeNB. The SCGconfiguration response message may further include a SeNB UE X2AP ID,which may be allocated by the SeNB and used to identify the UE betweenthe target MeNB and the SeNB.

At step 305, the target MeNB may send a handover request acknowledgementmessage to the source MeNB. The handover request acknowledgement messagemay include information indicating whether to maintain the SeNBunchanged. The target MeNB may allocate a DL TEID and DL transmissionlayer address of an S1 interface (an interface between the target MeNBand the SGW) to the bearer handed over to the target MeNB.

The target MeNB knows which bearer of the UE is at the SeNB and whetherthe bearer at the SeNB is split bearer or SCG bearer according to theinformation of bearer at the SeNB (i.e. which bearer are at the SeNB)and the information indicating whether the bearer at the SeNB is thesplit bearer or the SCG bearer in the handover request message receivedfrom the source MeNB at step 303. The target MeNB may allocate a DL TEIDand transmission layer address of an interface between the target MeNBand SGW to the split bearer. As for the SCG bearer, if the target MeNBdetermines to keep the SeNB unchanged, the target MeNB may not need toallocate DL TEID and DL transmission layer address to the SCG bearer. Ifthe target MeNB determines to handover the bearer at the SeNB to thetarget MeNB, the target MeNB may allocate the DL TEID and DLtransmission layer address of the S1 interface to the SCG bearer.

As for the bearer which may be handed over to the target MeNB and inneed of data forwarding, the target MeNB may allocate the TEID andtransmission layer address of the X2 interface, which may be used fordata forwarding.

The TEID and transmission layer address allocated by the target MeNB toeach bearer of the UE may be sent to the source MeNB via the handoverrequest acknowledgement message.

The target MeNB may allocate air interface resource to the bearer handedover to the target MeNB and send the configuration of the air interfaceto the source MeNB via the RRC container (i.e. the RRC container fromthe target MeNB).

As for the situation that the bearer at the SeNB is kept unchanged, ifthe target MeNB modifies the configuration at the SeNB and receives theRRC container from the SeNB, the target MeNB may send the RRC containerfrom the SeNB to the source MeNB via the handover requestacknowledgement message.

At step 306, the source MeNB may send a corresponding message to the UE.The source MeNB may send an RRC re-configuration message to the UE. TheRRC re-configuration message may include configuration information ofthe bearers handed over to the target MeNB, i.e. the RRC container fromthe target MeNB.

If the source MeNB receives from the target MeNB the informationindicating not to handover the SeNB, the RRC re-configuration messagemay not include information instructing the UE to delete the SCG. In thesituation that the SeNB may not be handed over, the source MeNB maymodify the configuration of the SCG according to the informationreceived from the target MeNB and send the RRC container from the SeNBto the UE.

If the source MeNB receives from the target MeNB the informationindicating handover the SeNB, the source MeNB may instruct the UE todelete the SCG while re-configuring the MCG and establish the bearers atthe source SCG to the target MeNB.

In a situation that the SeNB may be handed over, before the source MeNBsends the RRC re-configuration message to the UE, the source MeNB maysend a SeNB deletion request to the SeNB and notify the SeNB of the TEIDand transmission layer address of the data forwarding via the SeNBdeletion request. This process may be an existing process and may not bemain content of the present disclosure. The detailed technologydescription may be omitted.

The UE may send the RRC re-configuration response message to the targetMeNB.

The target MeNB may send a corresponding message to the MME.

In a situation that the SeNB may be handed over, the target MeNB maysend a path switch request message to the MME. The path switch requestmessage may include the DL TEID and DL transmission layer addressallocated by the target MeNB to each bearer.

In a situation that the SeNB may not be changed and the bearer at theSeNB is the split bearer, the target MeNB may send the path switchrequest message to the MME. The path switch request message may includethe DL TEID and DL transmission layer address allocated by the targetMeNB to each bearer.

In a situation that the SeNB may not be changed and the bearer at theSeNB is the SCG bearer, the target MeNB may send an Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) Radio Access Bearer (E-RAB)modification indication to the MME or send an enhanced path switchrequest message to the MME. The enhanced path switch request message isnot a name of a message. The enhanced path switch request message meansadding a new information element to the existing path switch requestmessage or the behavior of the MME may be different from that of the MMEin the prior art after the MME receives the enhanced path switch requestmessage. The E-RAB modification indication or the enhanced path switchrequest message may further include a Tracking Area Identity (TAI)and/or E-UTRAN Cell Global Identifier (ECGI) of the Pcell of the targetMeNB, and may further include: the TAI and/or ECGI of the Scell of theSeNB.

The E-RAB modification indication message may trigger establishment ofUE association S1 signaling connection between the target MeNB and theMME. The E-RAB modification indication message may include an MME UES1AP ID of the UE at the MME. The E-RAB modification indication messagemay include an eNB UE S1AP ID allocated by the target MeNB. The E-RABmodification indication message may include information of bearer to behanded over. The information of bearer maintained at the SeNB may notneed to be included in the E-RAB modification indication message. Afterthe MME receives the E-RAB modification indication message, the UEassociation S1 signaling connection between the target MeNB and the MMEmay be established. As for E-RAB, which may not be included in the E-RABmodification indication message, the MME may maintain the E-RAB and maynot release the E-RAB. The MME may send a modify bearer request messageto the SGW to request for modifying the handed over bearer. After theMME receives a modify bearer response message from the SGW, the MME maysend an E-RAB modification indication acknowledgement message to thetarget MeNB. The E-RAB modification indication acknowledgement messagemay include security context information, which may be used to update akey between the target MeNB and the UE. After the MME receives the E-RABmodification indication message, the MME may further make adetermination as to whether to re-select a SGW. When the MME makes thedetermination as to whether to re-select the SGW, the MME may considerthe TAI of the Pcell of the target MeNB, or may consider the TAI of thePcell of the target MeNB and the Scell of the SeNB simultaneously. IfSGW relocation is needed, the MME may send a create session requestmessage to the destination SGW. The create session request message mayinclude all bearers of the UE i.e. the bearer received from the targetMeNB which may need to be handed over, and the bearer which may not needto be handed over. The MME may know the information of the bearer, whichmay not need to be handed over, according to stored UE context. Thedestination SGW may allocate a UL TEID and UL transmission layer addressfor each bearer. The destination SGW may send a create session responsemessage to the MME. The MME may send an E-RAB modification indicationacknowledgement message to the target MeNB. In case of SGW relocation,the E-RAB modification indication acknowledgement message may not onlyinclude the UL TEID and UL transmission layer address of the handed overbearer, but also include the UL TEID and UL transmission layer addressof the bearer which may not be handed over Similar to the situationwithout SGW relocation, the E-RAB modification indicationacknowledgement message may include the security context, which may beused to update the key between the target MeNB and the UE.

The enhanced path switch request may include all the bearers e.g. thebearer which may need to be handed over and the bearer which may notneed to be handed over. After the MME receives the enhanced path switchrequest, as for the bearer which may not need to be handed over (suchas, the TEID and transmission layer address of the bearer are notchanged), the MME may not take the enhanced path switch request as anerror message and not trigger a de-activation process of the bearer. Ifthe TEID and transmission layer address of a bearer is not changed, theMME get to know that the bearer is not handed over. In an alternative,the enhanced path switch request may include indication information. Theindication information may indicate the bearer which may not be includedin the path switch request message, may not be released. After the MMEreceives the enhanced path switch request message, the MME may nottrigger the de-activation process of the bearer, which may not beincluded in the path switch request message according to the indicationinformation. The MME may send the modify bearer request message to theSGW to request for modifying the handed over bearers. After the MMEreceives the modify bearer response message from the SGW, the MME maysend the path switch request acknowledgement message to the target MeNB.After the MME receives the path switch request message, the MME may makea determination as to whether to re-select the SGW. When the MME makesthe determination as to whether to re-select the SGW, the MME mayconsider the TAI of the Pcell of the target MeNB, or may simultaneouslyconsider that TAI of the Pcell of the target MeNB and the TAI of theScell of the SeNB. If SGW relocation is needed, the MME may send thecreate session request message to the destination SGW. The createsession request message may include all the bearers of the UE i.e. thebearer received from the target MeNB which may need to be handed over,and the bearer which may not need to be handed over. The destination SGWmay allocate the UL TEID and transmission layer address for each bearer.The destination SGW may send the create session response message to theMME. The MME may send the path switch request acknowledgement message tothe target MeNB. In case of SGW relocation, the path switch requestacknowledgement message may not only include the UL TEID and ULtransmission layer address of the handed over bearer, but also includethe UL TEID and UL transmission layer address of the bearer which maynot be handed over.

The target MeNB may send a UE configuration completion message to theSeNB. The UE configuration completion message may include the MeNB UEX2AP ID between the target MeNB and the SeNB allocated by the targetMeNB for the UE. If before this block (such as block 304), the targetMeNB changed the configuration of the SeNB, the UE configurationcompletion message may include the SeNB UE X2AP ID, which may beallocated by the SeNB to identify the UE between the target MeNB and theSeNB.

If there is no configuration change procedure between the target MeNBand the SeNB before this block (such as block 304), the UE configurationcompletion message may include information which is used by the SeNB toidentify the UE. Then the SeNB can know for which UE there is inter-MeNBhandover. The information, which is used by the SeNB to identify the UE,may be received from the source MeNB. The information, which may be usedby the SeNB to identify the UE, may include the cell ID of the Scell atthe SeNB and the Cell Radio Network Temporary Identifier (C-RNTI) of theUE in the Scell. If there are multiple serving Scells at the SeNB,multiple pairs of cell ID of the Scell and C-RNTI may be included in theinformation. The information, which is used by the SeNB to identify theUE, may be the SeNB UE X2AP ID of the UE allocated by the SeNB. In casethe information, which is used by the SeNB to identify the UE includingthe SeNB UE X2AP ID, it may further include the ID of the source MeNBand/or the MeNB UE X2AP ID allocated by the source MeNB besides the SeNBUE X2AP ID of the UE allocated by the SeNB. A UE associated X2 signalingconnection between the target MeNB and the SeNB may be established withthis process.

As for the split bearer, the UE configuration completion message mayfurther include an E-RAB ID, the TEID and transmission layer addressallocated by the target MeNB. In case of SGW relocation, as for the SCGbearer, the UE configuration completion message may further include: theUL TEID and UL transmission layer address allocated by a new SGW. TheSeNB may store information received from the target MeNB and deleterelevant information of the source MeNB. If the SeNB receives a new Keyfrom the target MeNB, the SeNB may update the used key.

The source MeNB makes the target MeNB know the SeNB of the UE and theinformation to identify the UE at the SeNB via the step 303. So thetarget MeNB can send a message to a correct SeNB. The target MeNB maysend the information for identifying the UE at the SeNB to the SeNB. TheSeNB can know for which UE there is inter-MeNB handover. The SeNB mayperform correct modification and deletion to solve the above problemfour put forwarded in the present disclosure.

*118 optionally, the SeNB may further send the UE configurationcompletion acknowledgement message to the target MeNB.

The target MeNB may obtain the DL TEID and DL transmission layer addressof the X2 interface allocated by the SeNB to the split bearer via twomethods.

Method one: The source MeNB may notify the target MeNB of the DL TEIDand DL transmission layer address of the X2 interface allocated by theSeNB for the split bearer via block 303.

Method two: the SeNB may send the DL TEID and DL transmission layeraddress of the X2 interface allocated by the SeNB to the split bearervia the UE configuration completion acknowledgement message.

Therefore, the target MeNB may send DL data to the SeNB.

At step 307, the source MeNB may execute a handover process from thesource MeNB to the target MeNB and hand over the bearer at the SeNB tothe target MeNB. This flow may be the same as the existing handoverprocess from the MeNB to the eNB and may not be emphasis of the presentdisclosure. Therefore, detailed technical description may be omitted.

In the method shown in FIG. 3, the source MeNB may make an initialdetermination as to whether to maintain the SeNB and the target MeNB maymake a final determination as to whether to maintain the SeNB.Therefore, in the situation that the SeNB may not be handed over, it maybe ensured that the bearer at the SeNB is not released incorrectly inboth the UE side and the CN side, the deletion and re-establishment ofthe bearers at the SeNB may be avoided, the SGW relocation may besupported and the six technical problems mentioned above may be solved.

FIG. 4 may be a schematic diagram illustrating inter-MeNB handovermethod two in a small cell system. The main process of the method mayinclude that a source MeNB may send a handover request message to atarget MeNB. The target MeNB may make a determination as to whether tomaintain a SeNB and notify the source MeNB of the result of thedetermination. The source MeNB may send a corresponding message to theUE. After the target MeNB receives an RRC re-configuration responsemessage from the UE, the target MeNB may send a corresponding message tothe CN, so that the bearer of the UE at the SeNB may be maintained andmay not be released in both UE side and CN. The handover request andhandover response may respectively be an enhanced handover request andenhanced handover response message. The enhancement here doesn't mean aname of the message, but means that a new information element may beadded to the exiting handover request and handover response message.Specifically, the method shown in FIG. 4 may include following steps.

At step 401, the source MeNB may determine to hand over the UE to thetarget MeNB.

Step 402 to step 405 may be the same as step 303 to step 306, withoutgoing into the details.

With the above method shown in FIG. 4, the target MeNB may make adetermination as to whether to maintain the SeNB. In the situation thatthe SeNB may be maintained and may not be handed over, it may be ensuredthat the bearer of the UE at the SeNB may not be falsely released inboth UE side and CN side. The deletion and re-establishment of bearer atthe SeNB may be avoided, the SGW relocation may be supported and the sixtechnical problems mentioned above may be solved.

FIG. 5 may be a schematic diagram illustrating inter-MeNB handovermethod three in a small cell system. The main process of the method mayinclude: making, by a source MeNB, a determination as to whether tomaintain a SeNB and executing a corresponding process if thedetermination is yes. The bearer of the UE at the SeNB, which is nothanded over, may be maintained and may not be released in both UE sideand network side. The bearer, which is not handed over, may not need tobe deleted and re-established. Specifically, the method shown in FIG. 5may include following steps.

At step 501, the source MeNB may determine to hand over the UE to thetarget MeNB.

At step 502, the source MeNB may make a determination as to whether tomaintain the SeNB. If the source MeNB determines to hand over the bearerat the SeNB to target MeNB, block 506 may be executed. If the sourceMeNB determines to keep the SeNB unchanged, block 503 may be performed.

At this step, the source MeNB may make the determination as to whetherto change the SeNB according to the UE's measurement report. Forinstance, if the UE's measurement report shows that signal quality ofthe UE in a Scell of the SeNB is good enough, the source MeNB maydetermine that the SeNB may be kept unchanged. If the UE measure resultshows that the signal quality of the UE in the S cell of the SeNB is notgood enough, the source MeNB may determine to handover the bearer at theSeNB.

The source MeNB may make a determination as to whether to change theSeNB according to the UE's measurement report and whether there is an X2interface between the target MeNB and the SeNB. For instance, if theUE's measurement report shows that the signal quality of the S cell atthe SeNB is good enough and there is an X2 interface between the targetMeNB and the SeNB, the source MeNB may determine that the SeNB may bekept unchanged. If the UE's measurement report shows that the signalquality of the S cell at the SeNB is not good enough or there is no anX2 interface between the target MeNB and the SeNB, the source MeNB maydetermine to hand over the bearer at the SeNB. The source MeNB mayobtain whether there is an X2 interface between the target MeNB and theSeNB according to the configuration. The source MeNB may obtain whetherthere is an X2 interface between the target MeNB and the SeNB accordingto other methods without affecting the main content of the presentdisclosure.

When the source MeNB makes the determination, other factors (such as O&Mconfiguration) may be considered, without affecting the main content ofthe present disclosure.

Step 503 may be the same as step 303, which may not be repeated here.

At step 504, the target MeNB may send a handover request acknowledgementmessage to the source MeNB.

The target MeNB may allocate a DL TEID and DL transmission layer addressof an S1 interface (an interface between the target MeNB and the SGW) tothe bearer handed over to the target MeNB. The target MeNB knows whichbearer of the UE is at the SeNB and whether the bearer at the SeNB issplit bearer or SCG bearer according to the information of bearer at theSeNB (i.e. which bearer are at the SeNB) and information indicatingwhether the bearer at the SeNB is the split bearer or the SCG bearer inthe handover request message received from the source MeNB at step 503.The target MeNB may allocate a DL TEID and DL transmission layer addressof an interface between the target MeNB and SGW to the split bearer. Asfor the SCG bearer, the target MeNB may not need to allocate the DL TEIDand DL transmission layer address to the bearer. As for the bearer,which may be handed over to the target MeNB and in need of dataforwarding, the target MeNB may allocate the TEID and transmission layeraddress of the X2 interface for data forwarding.

The TEID and transmission layer address allocated by the target MeNB toeach bearer of the UE may be sent to the source MeNB via the handoverrequest acknowledgement message.

Before the target MeNB sends the handover request acknowledgementmessage to the source MeNB, the target MeNB may determine to modify theconfiguration of the bearer of the UE at the SeNB according to theconfiguration of the UE made by the target MeNB and/or UE capabilityinformation and/or other information, etc. If the target MeNB determinesto modify the configuration of the bearer at the SeNB, the target MeNBmay send an SCG configuration request message to the SeNB. The targetMeNB may obtain the SeNB of the UE according to the cell ID of the Scellof the UE at the SeNB and/or the ID of the SeNB in the handover requestmessage in step 503. The SCG configuration request message may includethe ID of the UE at the SeNB. The ID of the UE at the SeNB is the sameas that in block 303, without going into the details. The SCGconfiguration request message may further include the MeNB UE X2AP IDallocated by the target MeNB for the UE and used to identify the UEbetween the target MeNB and SeNB. The SCG configuration request messagemay be the existing SeNB modification request message or a new message.The SCG configuration request message may further include a new key ofthe UE in the Scell calculated by the target MeNB. The SeNB may send anSCG configuration response message to the target MeNB. The SCGconfiguration response message may include a Radio Resource Control(RRC) container containing the updated air interface configuration bythe SeNB. The SCG configuration response message may further include aSeNB UE X2AP ID, which may be allocated by the SeNB and used to identifythe UE between the target MeNB and the SeNB.

The target MeNB may allocate the air interface resource to the bearerhanded over to the target MeNB and send the configuration of the airinterface to the source MeNB via the RRC container (i.e. the RRCcontainer from the target MeNB)

As for the situation that the bearer at the SeNB is kept unchanged, ifthe target MeNB modifies the configuration at the SeNB and receives theRRC container from the SeNB, the target MeNB may send the RRC containersent from the SeNB to the source MeNB via the handover requestacknowledgement message.

At step 505, the source MeNB may send a corresponding message to the UE.The source MeNB may send an RRC re-configuration message to the UE. TheRRC re-configuration message may include configuration information ofthe bearer handed over to the target MeNB, i.e. the RRC container sentfrom the target MeNB.

If the source MeNB determines not to hand over the bearer at the SeNB,the RRC re-configuration message may not include information instructingthe UE to delete the SCG. In the situation that the SeNB may not behanded over, the source MeNB may modify the configuration of the SCGaccording to the information received from the target MeNB and send theRRC container sent from the SeNB to the UE.

If the source MeNB determines to hand over the bearer at the SeNB, thesource MeNB may indicate the UE to delete the SCG while re-configuringthe MCG and establish the bearers at the source SCG to the target MeNB.

In a situation that the SeNB may be handed over, before the source MeNBsends the RRC re-configuration message to the UE, the source MeNB maysend a SeNB deletion request to the SeNB and notify the SeNB of the TEIDand transmission layer address for the data forwarding via the SeNBdeletion request. This process may be an existing process and may not bemain content of the present disclosure. The detailed technologydescription may be omitted.

The UE may send the RRC re-configuration response message to the targetMeNB.

The target MeNB may send the corresponding message to the MME. Thespecific process between the target MeNB and the MME and the processbetween the MME and the SGW is the same as those described at step 306,without going into the details here.

The target MeNB may send a UE configuration completion message to theSeNB. The UE configuration completion message may include the MeNB UEX2AP ID between the target MeNB and the SeNB, which is allocated by thetarget MeNB to the UE. If before this block (such as block 504), thetarget MeNB changes the configuration of the SeNB, the UE configurationcompletion message may include the SeNB UE X2AP ID allocated by theSeNB, which is used to identify the UE between the target MeNB and theSeNB.

If there is no configuration change procedure between the target MeNBand the SeNB before this block (such as block 504), the UE configurationcompletion message may include information which is used by the SeNB toidentify the UE. Then, the SeNB can know for which UE there isinter-MeNB handover. The information, which is used by the SeNB toidentify the UE, may be received from the source MeNB. The information,which may be used by the SeNB to identify the UE, may include the cellID of the Scell at the SeNB and the Cell Radio Network TemporaryIdentifier (C-RNTI) of the UE in the Scell. If there are multipleserving Scells at the SeNB, multiple pairs of cell ID of the S cell andC-RNTI may be included in the information, which may be used by the SeNBto identify the UE. The information, which is used by the SeNB toidentify the UE is the SeNB UE X2AP ID of the UE allocated by the SeNB.The information, which is used by the SeNB to identify the UE, mayfurther include the ID of the source MeNB and/or the MeNB UE X2AP IDallocated by the source MeNB besides the SeNB UE X2AP ID of the UEallocated by the SeNB. A UE associated X2 signaling connection betweenthe target MeNB and the SeNB may be established with this process.

As for the split bearer, the UE configuration completion message mayfurther include an E-RAB ID, the TEID and transmission layer addressallocated by the target MeNB. In case of SGW relocation, as for the SCGbearer, the UE configuration completion message may further include: theUL TEID and UL transmission layer address allocated by a new SGW. TheSeNB may store information received form the target MeNB and deleterelevant information of the source MeNB. If the SeNB receives a new Keyfrom the target MeNB, the SeNB may update the used key.

The source MeNB may makes the target MeNB know the SeNB of the UE andthe information to identify the UE at the SeNB via the step 503. So thetarget MeNB can send a message to a correct SeNB. The target MeNB maysend the information for identifying the UE at the SeNB to the SeNB. TheSeNB can know for which UE there is inter-MeNB handover. The SeNB mayperform correct modification and deletion to solve the above problemfour put forwarded in the present disclosure.

Optionally, the SeNB may further send the UE configuration completionacknowledgement message to the target MeNB.

The target MeNB may obtain the DL TEID and DL transmission layer addressof the X2 interface allocated by the SeNB to the split bearers via twomethods.

Method one: The source MeNB may notify the target MeNB of the DL TEIDand DL transmission layer address of the X2 interface allocated by theSeNB for the split bearer via block 503.

Method two: the SeNB may send the DL TEID and DL transmission layeraddress of the X2 interface allocated by the SeNB to the split bearervia the UE configuration completion acknowledgement message.

Therefore, the target MeNB may send DL data to the SeNB.

Block 506 may be the same as block 307, without going into the details.

In the method shown in FIG. 5, the source MeNB may make a determinationas to whether to maintain the SeNB. In the situation that the SeNB maynot be handed over, it may be ensured that the bearer of the UE at theSeNB is not released incorrectly in both the UE side and the CN side,the deletion and re-establishment of the bearers at the SeNB may beavoided, the SGW relocation may be supported and the six technicalproblems mentioned above may be solved.

FIG. 6 may be a schematic diagram illustrating inter-MeNB handovermethod four in a small cell system. The main process of the method mayinclude that a target MeNB may notify a source MeNB of whether there isan X2 interface between the target MeNB and an SeNB. The source MeNB maymake a determination as to whether to maintain the SeNB. If the sourceMeNB determines to maintain the SeNB, a corresponding process may beexecuted to keep the bearer of the UE at the SeNB unreleased in both UEside and network side. Specifically, the method shown in FIG. 6 mayinclude following blocks.

At step 601, the source MeNB may determine to hand over the UE to thetarget MeNB.

Step 602 may be the same as step 303, without going into the details.

At step 603, the target MeNB may send a handover request acknowledgementmessage to the source MeNB. The handover request acknowledgement messagemay include: information indicating whether there is an X2 interfacebetween the target MeNB and the SeNB or information indicating whetherit may be feasible to maintain the SeNB. The target MeNB may make adetermination as to whether it may be feasible to maintain the SeNB. Forinstance, if there is an X2 interface between the target MeNB and theSeNB, it may be feasible to maintain the SeNB. If there is no an X2interface, it may not be feasible to maintain the SeNB. The target MeNBmay consider other information, such as O&M configuration when thetarget MeNB considers whether it is feasible.

The target MeNB may allocate a DL TEID and DL transmission layer addressof an S1 interface (an interface between the target MeNB and the SGW) tothe bearer handed over to the target MeNB. The target MeNB knows whichbearer of the UE is at the SeNB and whether the bearer at the SeNB issplit bearer or SCG bearer according to the information of bearer at theSeNB (i.e. which bearer are at the SeNB) and information indicatingwhether the bearer at the SeNB is the split bearer or the SCG bearer inthe handover request message received from the source MeNB at step 602.The target MeNB may allocate a DL TEID and DL transmission layer addressof an interface between the target MeNB and SGW to the split bearer. Asfor the SCG bearer, the target MeNB may not need to allocate the DL TEIDand DL transmission layer address to the bearer. As for the bearer,which may be handed over to the target MeNB and in need of dataforwarding, the target MeNB may allocate the TEID and transmission layeraddress of the X2 interface for data forwarding.

The TEID and transmission layer address allocated by the target MeNB toeach bearer of the UE may be sent to the source MeNB via the handoverrequest acknowledgement message.

At step 604, the source MeNB may make a determination as to whether tomaintain the SeNB. If the source MeNB determines to hand over the bearerat the SeNB to the target MeNB, block 606 may be executed. If the MeNBdetermines to keep the SeNB unchanged, block 605 may be executed.

The source MeNB may further make a determination as to whether to changethe SeNB according to the UE's measurement report and whether there isan X2 interface between the target MeNB and the SeNB or informationreceived from the target MeNB indicating whether it may be feasible tomaintain the SeNB. For instance, if the UE's measurement report showsthat the signal quality of the Scell at the SeNB is good enough andthere is an X2 interface between the target MeNB and the SeNB or it maybe feasible to maintain the SeNB, the source MeNB may determine that theSeNB may be kept unchanged. If the UE's measurement report shows thatthe signal quality of the Scell at the SeNB is not good enough or thereis no an X2 interface between the target MeNB and the SeNB or it may notbe feasible to maintain the SeNB, the source MeNB may determine to handover the bearer at the SeNB. The source MeNB may consider other factors(such as O&M configuration) when making the determination withoutaffecting the main content of the present disclosure.

If the source MeNB determines to keep the SeNB unchanged, the sourceMeNB may notify the target MeNB of maintaining the SeNB. The target MeNBmay release the DL TEID and DL transmission layer address of the S1interface allocated to the SCG bearer and the air interface resourceallocated to the SCG bearer.

As for the bearer maintained at the SeNB, the target MeNB may determineto modify the configuration of the bearer of the UE at the SeNBaccording to the configuration of the bearer of the UE made by thetarget MeNB and/or UE capability information or other information, etc.If the target MeNB determines to modify the configuration of the bearerat the SeNB, the target MeNB may send an SCG configuration requestmessage to the SeNB. The target MeNB may know the SeNB of the UEaccording to the cell ID of the S cell of the UE at the SeNB and/or IDof the SeNB in the handover request message at the block 602. The SCGconfiguration request message may include the ID of the UE at the SeNB,which may be the same as that at step 602, without going into thedetails. The SCG configuration request message may further include theMeNB UE X2AP ID, which may be allocated by the target MeNB to the UE andused to identify the UE between the target MeNB and SeNB. The SCGconfiguration request message may be the existing SeNB modificationrequest or a new message. The SCG configuration request message mayfurther include a new key of the UE in the Scell calculated by thetarget MeNB. The SeNB may send an SCG configuration response message tothe target MeNB. The SCG configuration response message may include aRadio Resource Control (RRC) container containing the updated airinterface configuration by the SeNB. The SCG configuration responsemessage may further include a SeNB UE X2AP ID, which may be allocated bythe SeNB and used to identify the UE between the target MeNB and theSeNB. If the target MeNB receives the RRC container from the SeNB, thetarget MeNB may send the RRC container received from the SeNB to thesource MeNB.

Block 605 may be the same as block 505, without going into the details.

At step 606, the source MeNB may execute other processes of the handoverfrom the source MeNB to the target MeNB and hand over the bearer at theSeNB to the target MeNB. This flow may be the same as the existinghandover process from the MeNB to the eNB. For instance, the source MeNBmay send a SeNB release request to the SeNB and the source MeNB may sendthe RRC re-configuration message to the UE, etc. This flow may not beemphasis of the present disclosure. Therefore, detailed technicaldescription may be omitted.

In the method shown in FIG. 6, the source MeNB may make a determinationas to whether to maintain the SeNB. In the situation that the SeNB maynot be handed over, v, the deletion and re-establishment of the bearerat the SeNB may be avoided, the SGW relocation may be supported and thesix technical problems mentioned above may be solved.

The technical scheme of the present disclosure may be further describedin detail via several embodiments.

Embodiment One

The signaling flow of the embodiment one of the present disclosure maybe shown in FIG. 7. The method one to method four in FIGS. 3 to 6 mayrespectively have described how to make a determination as to whether tomaintain the SeNB in detail. Therefore, this embodiment will notdescribe how to make a determination as to whether to maintain the SeNBin detail. The emphasis of this embodiment may be describing how tosolve the problem two to problem six put forwarded in the presentdisclosure. The flow shown in FIG. 7 may include following steps.

At step 701, a source MeNB may send a handover request message to atarget MeNB. The handover request message may include: information of asource SeNB, ID of a UE at the SeNB, bearer of the UE at the SeNB andwhether the bearer is split bearer or SCG bearer, etc. This step may bethe same as step 303, without going into the details.

For inter-MeNB handover without SeNB change, the source SeNB will alsobe the target SeNB. Therefore, the source SeNB, the target SeNB and theSeNB has the same meaning i.e. it refers to the secondary eNB thatallocate radio resource for the UE over the air interface besides theMeNB before and after inter-MeNB handover.

At step 702, the target MeNB may send a handover request acknowledgementmessage to the source MeNB.

Corresponding to the method that the target MeNB may make adetermination as to whether to keep the SeNB unchanged, the handoverrequest acknowledgement message may further include: informationindicating that the SeNB may be kept unchanged.

The target MeNB may allocate a DL TEID and DL transmission layer addressof an S1 interface (an interface between the target MeNB and the SGW) tothe bearer handed over to the target MeNB.

The target MeNB may know which bearer of the UE is at the SeNB andwhether the bearer at the SeNB is the split bearer or SCG beareraccording to the information indicating bearer at the SeNB (i.e. whichbearer is at the SeNB) and the information indicating whether the bearerat the SeNB is the split bearer or the SCG bearer in the handoverrequest message received from the source MeNB at step 701. The targetMeNB may allocate a DL TEID and DL transmission layer address of aninterface between the target MeNB and the SGW to the split bearer. Asfor the SCG bearer, if the target MeNB determines to keep the SeNBunchanged, the target MeNB may not need to allocate DL TEID and DLtransmission layer address to the SCG bearer. If the target MeNBdetermines to hand over the bearer from the SeNB to the target MeNB, thetarget MeNB may allocate the DL TEID and DL transmission layer addressof the S1 interface to the SCG bearer.

As for the bearer, which may be handed over to the target MeNB and incase data forwarding is needed, the target MeNB may allocate the TEIDand transmission layer address of the X2 interface used for dataforwarding.

The TEID and transmission layer address allocated by the target MeNB toeach bearer of the UE may be sent to the source MeNB via the handoverrequest acknowledgement message.

The target MeNB may allocate air interface resource to the bearer handedover to the target MeNB and send the configuration of the air interfaceto the source MeNB via the RRC container (i.e. the RRC container sentfrom the target MeNB).

The source MeNB makes the target MeNB know which bearer of the UE is atthe SeNB and whether the bearer at the SeNB is split bearer or the SCGbearer via step 701. The target MeNB may know which bearer is kept atthe SeNB according to a determination that the bearer at the SeNB iskept unchanged made by the target MeNB or made by the source MeNB andinformed by the source MeNB. The target MeNB can correctly configureresource for different bearer of the UE to solve the problem two andproblem three put forwarded in the present disclosure.

At step 703, the source MeNB may send an RRC re-configuration message tothe UE.

If the SeNB is not handed over, the source MeNB may send the RRCre-configuration message to the UE. And the RRC re-configuration messagedoes not include information instructing the UE to delete the SCG. Inthe situation that the SeNB may not be handed over, the source MeNB maydetermine to modify the configuration of the SCG according to theinformation received from the target MeNB.

If the SeNB is handed over, the source MeNB may instruct the UE todelete the SCG while re-configuring the MCG and establish the bearer inthe source SCG to the target MeNB.

At step 704, the source MeNB may send Sequence Number (SN) status to thetarget MeNB.

The source MeNB may start to perform data forwarding.

In the present disclosure, there may not be an absolute order betweenblock 703 and block 704. That is, the source MeNB may send the SN statusto the target MeNB and perform data forwarding first and then send theRRC re-configuration request message to the UE.

At step 705, the UE may send an RRC re-configuration response message tothe target MeNB.

At step 706, the target MeNB sends a path switch request or E-RABmodification indication message to the MME.

In a situation that the SeNB may be handed over, the target MeNB maysend the path switch request message to the MME. The path switch requestmessage may include the DL TEID and DL transmission layer addressallocated by the target MeNB to each bearer handed over to the targetMeNB.

In a situation that the SeNB may not be changed and the bearer at theSeNB is the split bearer, the target MeNB may send the path switchrequest message to the MME. The path switch request message may includethe DL TEID and DL transmission layer address allocated by the targetMeNB to each bearer.

In a situation that the SeNB may not be changed and the bearer at theSeNB is the SCG bearer, the target MeNB may send an Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) Radio Access Bearer (E-RAB)modification indication message to the MME or send an enhanced pathswitch request message to the MME. The enhanced path switch requestmessage is not the message name Instead, the enhanced path switchrequest message may be adding a new information element to the existingpath switch request message or alternatively the MME behavior isdifferent from the prior art when the MME receives the message. TheE-RAB modification indication or the enhanced path switch requestmessage may further include a Tracking Area Identity (TAI) and/orE-UTRAN Cell Global Identifier (ECGI) of the Pcell in the target MeNB.The E-RAB modification indication or the enhanced path switch requestmessage may include a TAI and/or ECGI of the Scell in the SeNB. If theUE has multiple Scells at the SeNB, the E-RAB modification indication orthe enhanced path switch request message may further include: multipleTAIs and/or ECGIs.

The E-RAB modification indication message may be used to triggerestablishment of UE associated S1 signaling connection between thetarget MeNB and the MME. The E-RAB modification indication message mayinclude an MME UE S1AP ID of the UE at the MME. The E-RAB modificationindication message may include an eNB UE S1AP ID allocated by the targetMeNB. The E-RAB modification indication message may include informationof bearer to be handed over. The information of bearer maintained at theSeNB may not need to be included in the E-RAB modification indicationmessage. After the MME receives the E-RAB modification indicationmessage, the UE associated S1 signaling connection between the targetMeNB and the MME may be established. As for E-RAB which is not includedin the E-RAB modification indication message, the MME may maintain theE-RAB unreleased. The MME may send a modify bearer request message tothe SGW to request for modifying DL tunnel of the handed over bearer.After the MME receives a modify bearer response message from the SGW,the MME may send an E-RAB modification indication acknowledgementmessage to the target MeNB. The E-RAB modification indicationacknowledgement message may include security context information, whichmay be used to update a key between the target MeNB and the UE. Afterthe MME receives the E-RAB modification indication message, the MME mayfurther make a determination as to whether to re-select a SGW. When theMME makes the determination as to whether to re-select the SGW, the MMEmay consider the TAI of the Pcell in the target MeNB, or may considerthe TAI of the Pcell of the target MeNB and the TAI of the Scell in theSeNB. If SGW relocation is needed, the MME may send an create sessionrequest message to the destination SGW. The create session requestmessage may contain all bearers of the UE which include information ofbearer received from the target MeNB which may need to be handed overand information of bearer which may not need to be handed over. The MMEmay know the information of the bearer, which may not need to be handedover, according to stored UE contexts. The destination SGW may allocatea UL TEID and UL transmission layer address for each bearer. Thedestination SGW may send a create session response message to the MME.The MME may send an E-RAB modification indication acknowledgementmessage to the target MeNB. In case of SGW relocation, the E-RABmodification indication acknowledgement message may not only include theUL TEID and UL transmission layer address of the handed over bearer, butalso include the UL TEID and UL transmission layer address of the bearerwhich may not be handed over. Similar to the situation without SeNBrelocation, the E-RAB modification indication acknowledgement messagemay include the security context, which may be used to update the keybetween the target MeNB and the UE.

The enhanced path switch request may include all the bearers of the UEe.g. the bearer which may need to be handed over and the bearer whichmay not need to be handed over. After the MME receives the enhanced pathswitch request, as for the bearer which may not need to be handed over(such as, the TEID and transmission layer address of the bearer have nochange) and the MME may not trigger a de-activation process for thebearer. In an alternative, the enhanced path switch request may includeindication information, which indicates that the bearer not included inthe path switch request message is not released. After the MME receivesthe enhanced path switch request message, the MME does not trigger thede-activation process of the bearer which is not included in the pathswitch request message according to the indication information. The MMEmay send the modify bearer request message to the SGW to request formodifying the handed over bearer. After the MME receives the modifybearer response message from the SGW, the MME may send the path switchrequest acknowledgement message to the target MeNB. After the MMEreceives the path switch request message, the MME may further make adetermination as to whether to re-select a SGW. When the MME makes thedetermination as to whether to re-select the SGW, the MME may considerthe TAI of the Pcell of the target MeNB, or may consider the TAI of thePcell of the target MeNB and the Scell of the SeNB simultaneously. IfSGW relocation is needed, the MME may send a create session requestmessage to the destination SGW. The create session request message mayinclude all bearers of the UE i.e. the bearer received from the targetMeNB which may need to be handed over, and the bearer which may not needto be handed over. The MME may know the information of the bearer, whichmay not need to be handed over, according to stored UE context. Thedestination SGW may allocate a UL TEID and UL transmission layer addressfor each bearer. The destination SGW may send a create session responsemessage to the MME. The MME may send a path switch requestacknowledgement message to the target MeNB. In case of SGW relocation,the E-RAB modification indication acknowledgement message may not onlyinclude the UL TEID and UL transmission layer address of the handed overbearer, but also include the UL TEID and UL transmission layer addressof the bearer which may not be handed over.

At step 707, the MME sends an E-RAB modification indicationacknowledgement or path switch request acknowledgement message to thetarget MeNB.

If the E-RAB modification indication is received at step 706, the E-RABmodification indication acknowledgement may be sent at this step. If thepath switch request is received at step 706, the path switch requestacknowledgement may be sent at this step.

In case of SGW relocation, the E-RAB modification indicationacknowledgement or path switch request acknowledgement message mayfurther include the UL TEID and UL transmission layer address of bearer,which is not handed over.

The source MeNB makes the target MeNB know which bearer of the UE is atthe SeNB and whether the bearer at the SeNB is split bearer or SCGbearer via block 701. According to a determination that the bearer atthe SeNB is kept unchanged made by the target MeNB or made by the sourceMeNB and informed by the source MeNB, the target MeNB can send asuitable message to the MME to notify the MME of bearer which need to behanded over and bearer which may not need to be handed over. Therefore,it may be avoided that the MME may falsely release some bearers. In caseof SGW relocation is needed, the MME can inform the SGW to allocate theUL TEID and UL transmission layer address to the bearer which may notneed to be handed over. Therefore, the problem five and problem six putforwarded in the present disclosure may be solved.

At step 708, the target MeNB may send a UE configuration completionmessage to the SeNB. The UE configuration completion message may includethe MeNB UE X2AP ID between the target MeNB and the SeNB allocated bythe target MeNB to the UE.

The UE configuration completion message may include information, whichis used by the SeNB to identify the UE. The information, which may beused by the SeNB to identify the UE, may be received from the sourceMeNB. The information, which is used by the SeNB to identify the UE atthe SeNB, may include the cell ID of the Scell at the SeNB and the CellRadio Network Temporary Identifier (C-RNTI) of the UE in the Scell. Ifthere may be multiple serving Scells at the SeNB, multiple pairs of cellID of the Scell and C-RNTI may be included in the information, which isused by the SeNB to identify the UE. The information, which is used bythe SeNB to identify the UE, may be the SeNB UE X2AP ID of the UEallocated by the SeNB. In case the information, which is used by theSeNB to identify the UE is the SeNB UE X2AP ID, it may further includethe ID of the source MeNB and/or the MeNB UE X2AP ID allocated by thesource MeNB besides the SeNB UE X2AP ID of the UE allocated by the SeNB.

*204 as for the split bearer, the UE configuration completion messagemay further include an E-RAB ID, the TEID and transmission layer addressallocated by the target MeNB to each bearer.

In case of SGW relocation, as for the SCG bearer, the UE configurationcompletion message may further include: the UL TEID and UL transmissionlayer address allocated by a new SGW.

The SeNB may store information received form the target MeNB and deleterelevant information of the source MeNB. If the SeNB receives a new Keyfrom the target MeNB, the SeNB may update the used key.

A UE associated X2 signaling connection between the target MeNB and theSeNB may be established with this process.

Optionally, the SeNB may further send the UE configuration completionacknowledgement message to the target MeNB.

The target MeNB may obtain the DL TEID and DL transmission layer addressof the X2 interface allocated by the SeNB to the split bearer via twomethods.

Method one: The source MeNB may notify the target MeNB of the DL TEIDand DL transmission layer address of the X2 interface allocated by theSeNB to the split bearer via block 701.

Method two: the SeNB may send the DL TEID and DL transmission layeraddress of the X2 interface allocated by the SeNB to the split bearervia the UE configuration completion acknowledgement message.

The source MeNB makes the target MeNB know the SeNB of the UE andinformation at the SeNB for identifying the UE at the SeNB via block701. So the target MeNB can send a message to a correct SeNB. The targetMeNB sends the information for identifying the UE at the SeNB to theSeNB. The SeNB can know for which UE there is inter-MeNB handover. TheSeNB may perform correct bearer modification and deletion to solve theproblem four put forwarded in the present disclosure.

Various problems in the inter-MeNB handover process may be solved viathis embodiment, to make the inter-MeNB handover without SeNB changefeasible.

Embodiment Two

The signaling flow of the embodiment two of the present disclosure maybe shown in FIG. 8. The method one to method four in FIGS. 3 to 6 mayrespectively have described how to make a determination as to whether tomaintain the SeNB in detail. Therefore, this embodiment will notdescribe how to make a determination as to whether to maintain the SeNBin detail. The emphasis of this embodiment may be describing how tosolve the problem two to problem six put forwarded in the presentdisclosure. The flow shown in FIG. 8 may include following steps.

At step 801, a source MeNB sends a handover request message to a targetMeNB. The handover request message may include: information of a sourceSeNB, ID of a UE at the SeNB, bearer of the UE at the SeNB and/orwhether the bearer is split bearer or SCG bearer. This step is the sameas step 303, without going into the details.

For inter-MeNB handover without SeNB change, the source SeNB will alsobe the target SeNB. Therefore, the source SeNB, the target SeNB and theSeNB has the same meaning i.e. it refers to the secondary eNB thatallocate radio resource for the UE over the air interface besides theMeNB before and after inter-MeNB handover.

At step 802, the target MeNB sends an SCG configuration request to theSeNB. The target MeNB can know the SeNB of the UE according to the ID ofthe SeNB or the cell ID of the Scell in the SeNB received at step 801.

The target MeNB may calculate a new Key for the UE at the SeNB and thetarget MeNB may send the new Key of the UE to the SeNB via the SCGconfiguration request.

The SCG configuration request may include information which is used bythe SeNB to identify the UE. Therefore, The SeNB can know for which UEthere is inter-MeNB handover. The information, which is used by the SeNBto identify the UE, may be received from the source MeNB. The specificinformation is the same as that described at step 708, without goinginto the details.

The target MeNB may modify the configuration of the bearer at the SeNBvia the SCG configuration request message.

The SCG configuration may be a new message or may be implemented viaenhancing the existing SeNB modification request procedure.

The UE associated X2 signaling connection between the target MeNB andthe SeNB may be established via the SCG configuration message.

The source MeNB makes the target MeNB know the SeNB of the UE andinformation at the SeNB for identifying the UE at the SeNB via step 801.The target MeNB sends a message to a correct SeNB and sends theinformation for identifying the UE at the SeNB to the SeNB. The SeNB canknow for which UE there is inter-MeNB handover. The SeNB performscorrect modification and deletion to solve the problem four putforwarded in the present disclosure.

At step 803, the SeNB sends an SCG configuration response message to thetarget MeNB.

The SCG configuration response message may include a SeNB X2AP IDbetween the SeNB and target MeNB allocated by the SeNB.

This embodiment may include this block or may not include this block.

If a SeNB modification request is sent at step 802, a SeNB modificationrequest acknowledgement may be sent at this step.

If the configuration of the bearer at the SeNB is modified, the SeNB maysend re-configuration information over the air interface to the targetMeNB via carrying the RRC container (i.e. the RRC container sent fromthe SeNB) in the SCG configuration response.

The SCG configuration response message may include the information toindicate that the UE context is kept. The UE context is kept doesn'texclude that the UE context may be updated. The SeNB behavior may bedifferent when the SeNB receives SCG configuration request message, e.g.for Rel-13 SeNB, the SeNB keeps the UE context and may update someinformation or update some bearer configuration, while for Rel-12 SeNB,the SeNB creates UE context according to the information received in SCGconfiguration request message and configure bearers. If the SeNB keepsthe UE context, the SeNB includes the indication information of keepingUE context in SCG configuration response message.

At step 804, the target MeNB sends a handover request acknowledgementmessage to the source MeNB. Corresponding to the method that the targetMeNB may make a determination as to whether to keep the SeNB unchanged,the handover request acknowledgement message may further include:information indicating that the SeNB may be kept unchanged.

The source MeNB may decide not to trigger SeNB release and/or UE contextrelease procedure. In case the source MeNB receives the informationindicating that the SeNB may be kept unchanged from the target MeNB, thesource MeNB may not trigger SeNB release and/or UE context releaseprocedure.

The target MeNB may allocate a DL TEID and transmission layer addressover an S1 interface (an interface between the target MeNB and the SGW)for the bearer handed over to the target MeNB.

The target MeNB may know which bearer of the UE is at the SeNB andwhether the bearer at the SeNB is the split bearer or SCG beareraccording to the information indicating bearer at the SeNB (i.e. whichbearer is at the SeNB) and the information indicating whether the bearerat the SeNB is the split bearer or the SCG bearer in the handoverrequest message received from the source MeNB at step 801. The targetMeNB may allocate a DL TEID and DL transmission layer address of aninterface between the target MeNB and SGW to the split bearer. As forthe SCG bearer, if the target MeNB decides to keep the SeNB unchanged,the target MeNB may not need to allocate DL TEID and DL transmissionlayer address to the SCG bearer. If the target MeNB decides to hand overthe bearer at the SeNB to the target MeNB, the target MeNB may allocatethe DL TEID and DL transmission layer address of the S1 interface to theSCG bearer.

As for the bearer, which may be handed over to the target MeNB and incase data forwarding is needed, the target MeNB may allocate the TEIDand transmission layer address of the X2 interface used for dataforwarding.

The TEID and transmission layer address allocated by the target MeNB toeach bearer of the UE may be sent to the source MeNB via the handoverrequest acknowledgement message.

The target MeNB may allocate air interface resource to the bearer handedover to the target MeNB and send the configuration of the air interfaceto the source MeNB via the RRC container (i.e. the RRC container sentfrom the target MeNB).

If the bearer at the SeNB is re-configured, the target MeNB may send theRRC container (i.e. the RRC container sent from the SeNB) received fromthe SeNB to the source MeNB.

The source MeNB makes the target MeNB know which bearer of the UE is atthe SeNB and whether the bearer at the SeNB is the split bearer or theSCG bearer via block 801. The target MeNB may know which bearer is keptat the SeNB according to a determination that the bearer at the SeNB iskept unchanged made by the target MeNB or made by the source MeNB andinformed by the source MeNB. The target MeNB may correctly configureresource for different bearer of the UE to solve the problem two andproblem three put forwarded in the present disclosure.

If the target MeNB receives the indication information of keeping UEcontext from the SeNB, the target MeNB sends the information to thesource MeNB. The target MeNB sends the indication information of keepingUE context to the source MeNB by handover request acknowledge message.The source MeNB decides whether trigger UE context release in SeNB basedon the received information. For example, the source MeNB does nottrigger SeNB release and/or UE context release if the source MeNBreceives the indication information of keeping UE context. If the sourceMeNB doesn't receive the indication information of keeping UE contextand/or the information of keeping SeNB unchanged, the source MeNB maytrigger the SeNB release and/or UE context release procedure.

At step 805, the source MeNB may send an RRC re-configuration message tothe UE.

If the SeNB is not handed over, the source MeNB may send the RRCre-configuration message to the UE and the RRC re-configuration messagedoes not include information instructing the UE to delete the SCG. Inthe situation that the SeNB may not be handed over, the source MeNB maydetermine to modify the configuration of the SCG according to theinformation received from the target MeNB. The source MeNB may send aRRC container received from the target MeNB which is constructed by theSeNB to the UE. At the same time, the source MeNB may send a second RRCcontainer received from the target MeNB which is constructed by thetarget MeNB to the UE. The former container may include there-configuration information of the bearer at the SeNB and the lattercontainer may include the configuration information of the bearer handedover to the target MeNB.

If the SeNB is handed over, the source MeNB may instruct the UE todelete the SCG while re-configuring the MCG and establish the bearer atthe source SCG to the target MeNB.

At step 806, the source MeNB may send SN status to the target MeNB.

The source MeNB may start to perform data forwarding.

In the present disclosure, there may not be an absolute order betweenblock 805 and block 806. That is, the source MeNB may send the SN statusto the target MeNB and perform data forwarding first and then send theRRC re-configuration message to the UE.

Step 807 to step 809 may be the same as block 705 to 707, without goinginto the details.

At step 810, the target MeNB may send a UE configuration completionmessage to the SeNB. The UE configuration completion message may includethe MeNB UE X2AP ID between the target MeNB and the SeNB allocated bythe target MeNB to the UE.

The UE configuration completion message may further include a SeNB X2APID between the SeNB and target MeNB allocated by the SeNB.

As for the split bearer, the UE configuration completion message mayfurther include an E-RAB ID, the TEID and transmission layer addressallocated by the target MeNB to each bearer.

In case of SGW relocation, as for the SCG bearer, the UE configurationcompletion message may further include: an E-RAB ID of the SCG, the ULTEID and UL transmission layer address allocated by a new SGW.

The SeNB may store information received from the target MeNB and deleterelevant information of the source MeNB.

Optionally, the SeNB may further send the UE configuration completionacknowledgement message to the target MeNB.

The target MeNB may obtain the DL TEID and DL transmission layer addressof the X2 interface allocated by the SeNB to the split bearer via twomethods.

Method one: The source MeNB may notify the target MeNB of the DL TEIDand DL transmission layer address of the X2 interface allocated by theSeNB to the split bearer via block 801.

Method two: the SeNB may send the DL TEID and DL transmission layeraddress of the X2 interface allocated by the SeNB to the split bearervia the UE configuration completion acknowledgement message.

Various problems in the inter-MeNB handover process may be solved viathis embodiment, to make inter-MeNB handover without SeNB changefeasible.

Embodiment Three

The signaling flow of the embodiment three of the present disclosure maybe shown in FIG. 9. The method one to method four in FIGS. 3 to 6 mayrespectively have described how to make a determination as to whether tomaintain the SeNB in detail. Therefore, this embodiment will notdescribe how to make a determination as to whether to maintain the SeNBin detail. The emphasis of this embodiment may be describing how tosolve the problem two to problem six put forwarded in the presentdisclosure. The flow shown in FIG. 9 may include following blocks.

At step 901, a source MeNB may send a handover request message to atarget MeNB. This step is the same as at step 303, without going intothe details.

For inter-MeNB handover without SeNB change, the source SeNB will alsobe the target SeNB. Therefore, the source SeNB, the target SeNB and theSeNB has the same meaning i.e. it refers to the secondary eNB thatallocate radio resource for the UE over the air interface besides theMeNB before and after inter-MeNB handover.

At step 902, the target MeNB may send an SCG configuration request tothe SeNB. This step is the same as step 802, without going into thedetails.

At step 903, the SeNB may send an SCG configuration response message tothe target MeNB.

The SCG configuration response message may include a SeNB X2AP IDbetween the SeNB and target MeNB allocated by the SeNB.

The SeNB may re-allocate the TEID and/or transmission layer address tothe bearer at the SeNB. That is, the SeNB may allocate a new TEID and/ortransmission layer address, release the original TEID and/ortransmission layer address and send the TEID and/or transmission layeraddress corresponding to each E-RAB ID to the target MeNB via the SCGconfiguration response message. The newly-allocated TEID and/ortransmission layer address may only be allocated for the SCG bearer atthe SeNB.

If a SeNB modification request is sent at step 902, a SeNB modificationrequest acknowledgement may be sent at this step.

If the configuration of the bearer at the SeNB is modified, the SeNB maysend re-configuration information of the air interface to the targetMeNB via carrying the RRC container (i.e. the RRC container sent fromthe SeNB) in the SCG configuration response.

The SCG configuration response message may include the information toindicate that the UE context is kept. The UE context is kept doesn'texclude that the UE context may be updated. The SeNB behavior may bedifferent when the SeNB receives SCG configuration request message, e.g.for Rel-13 SeNB, the SeNB keeps the UE context and may update someinformation or update some bearer configuration, while for Rel-12 SeNB,the SeNB creates UE context according to the information received in SCGconfiguration request message and configure bearers. If the SeNB keepsthe UE context, the SeNB includes the indication information of keepingUE context in SCG configuration response message.

At step 904, the target MeNB may send a handover request acknowledgementmessage to the source MeNB.

Corresponding to the method that the target MeNB may determine to keepthe SeNB unchanged, the handover request acknowledgement message mayfurther include: information indicating that the SeNB is kept unchanged.

The source MeNB may decide not to trigger SeNB release and/or UE contextrelease procedure. In case the source MeNB receives the informationindicating that the SeNB may be kept unchanged from the target MeNB, thesource MeNB may not trigger SeNB release and/or UE context releaseprocedure.

The target MeNB may allocate a DL TEID and DL transmission layer addressof an S1 interface (an interface between the target MeNB and the SGW) tothe bearer handed over to the target MeNB.

According to information indicating which bearer is at the SeNB andinformation indicating whether the bearer at the SeNB is the splitbearer or the SCG bearer in the handover request message received fromthe source MeNB at step 901, the target MeNB can know which bearer ofthe UE is at the SeNB and whether the bearer at the SeNB is the splitbearer or SCG bearer. The target MeNB may allocate a DL TEID and DLtransmission layer address of an interface between the target MeNB andSGW to the split bearer. As for the SCG bearer, if the target MeNBdetermines to keep the SeNB unchanged, the target MeNB may not need toallocate DL TEID and DL transmission layer address to the SCG bearer.The target MeNB may send the TEID and/or transmission layer address,which may be re-allocated by the SeNB and received from the SeNB at step903 to the source MeNB. If the target MeNB determines to handover thebearer at the SeNB to the target MeNB, the target MeNB may allocate theDL TEID and transmission layer address of the S1 interface to thebearer.

As for the bearer that are handed over to the target MeNB and in casedata forwarding is needed, the target MeNB may allocate the TEID andtransmission layer address of the X2 interface for data forwarding.

The TEID and transmission layer address allocated by the target MeNB toeach bearer of the UE may be sent to the source MeNB via the handoverrequest acknowledgement message. As for the SCG bearer, the target MeNBmay send the TEID and/or transmission layer address re-allocated by theSeNB to the source MeNB via a handover request acknowledgement message.

The target MeNB may allocate air interface resource to the bearer handedover to the target MeNB and send the configuration of the air interfaceto the source MeNB via the RRC container (i.e. the RRC container fromthe target MeNB).

If the bearer at the SeNB are re-configured, the target MeNB may sendthe RRC container (i.e. the RRC container from the SeNB) received fromthe SeNB to the source MeNB.

The source MeNB makes the target MeNB know which bearer of the UE is atthe SeNB and whether the bearer at the SeNB is the split bearer or theSCG bearer via block 901. The target MeNB can know which bearer may bekept at the SeNB according to a determination that the bearer at theSeNB is kept unchanged made by the target MeNB or made by the sourceMeNB and informed by the source MeNB. The target MeNB can correctlyconfigure resource for different bearer of the UE to solve the problemtwo and problem three put forwarded in the present disclosure.

If the target MeNB receives the indication information of keeping UEcontext from the SeNB, the target MeNB sends the information to thesource MeNB. The target MeNB sends the indication information of keepingUE context to the source MeNB by handover request acknowledge message.The source MeNB decides whether trigger UE context release in SeNB basedon the received information. For example, the source MeNB does nottrigger SeNB release and/or UE context release if the source MeNBreceives the indication information of keeping UE context. If the sourceMeNB doesn't receive the indication information of keeping UE contextand/or the information of keeping SeNB unchanged, the source MeNB maytrigger the SeNB release and/or UE context release procedure.

Block 905 to block 907 may be the same as block 805 to 807, withoutgoing into the details.

At step 908, the target MeNB may send the path switch request message tothe MME. The path switch request message may include the information ofthe bearer handed over from the source MeNB to the target MeNB. As forthe SCG bearer, since the DL TEID and/or DL transmission layer addressof the SCG bearers may be re-allocated by the SeNB, the path switchrequest message may further include the information of SCG bearer, whichmay be maintained at the SeNB and may not be handed over.

At step 909, the MME may send the path switch request acknowledgementmessage to the target MeNB.

Block 910 may be the same as block 810, without going into the details.

Various problems in the inter-MeNB handover process may be solved viathis embodiment, to make inter-MeNB handover without SeNB changefeasible.

Corresponding to the above method, an example of the present disclosuremay further provide an inter-MeNB handover device in a small cellsystem. As shown in FIG. 10, the device may include: a processor 1000and a transceiver 1010. The processor 1000 may control all of theoperations performed by the inter-MeNB handover device. The processor1000 may include: a determination module 1002 and a handover module1004. The determination module 1002 may be to make a determination as towhether to maintain a SeNB when handover is performed. The handovermodule 1004 may be to trigger different handover processes according toa result of the determination as to whether to maintain the SeNB.

The transceiver 1010 may be configured to communicate at least a signalwith other communication device or an entity in the small cell system.

However, the controller 1000 and the transceiver 1010 are notnecessarily implemented as separate devices, respectively, but may beimplemented in a single unit in the form of, e.g., a single chip.

The foregoing description may only describe preferred embodiments of thepresent invention and may not be used for limiting the protection scopethereof. Any modification, equivalent substitution, or improvement madewithout departing from the spirit and principle of the present inventionshould be covered by the protection scope of the present invention.

The invention claimed is:
 1. An inter-master enhanced NodeB (MeNB)handover method to a target MeNB from a source MeNB which providesdual-connectivity together with a secondary eNB (SeNB), the methodcomprising: receiving, by the target MeNB, a handover request messagefrom the source MeNB, wherein the handover request message comprises anidentity (ID) of a user equipment (UE) at the SeNB and an eNB ID of theSeNB; sending, by the target MeNB to the SeNB, a configuration requestmessage including the ID of the UE at the SeNB; sending, by the targetMeNB to the source MeNB, a handover request acknowledge messageindicating that the SeNB is kept unchanged; and sending, by the targetMeNB, a path switch request message to a mobile management entity (MME).2. The method according to claim 1, further comprising: as for a splitbearer at the SeNB, allocating, by the target MeNB, a down link (DL)tunnel endpoint identifier (TEID) and DL transmission layer address usedbetween the target MeNB and a serving gateway (SGW) to the split bearerat the SeNB, and sending, by the target MeNB, the DL TEID and DLtransmission layer address to the source MeNB via a handover requestacknowledgement message; or as for a SCG bearer at the SeNB, notallocating, by the target MeNB, the DL TEID and DL transmission layeraddress to the SCG bearers and sending an evolved universal terrestrialradio access network (E-UTRAN) radio access bearer (E-RAB) modificationindication or a path switch request message to a mobile managemententity (MME), wherein the E-RAB modification indication or the pathswitch request message includes a tracking area identity (TAI) orE-UTRAN cell global identifier (ECGI) of a primary cell (Pcell) of thetarget MeNB, and a TAI or ECGI of a Scell at the SeNB, and wherein aradio resource control (RRC) re-configuration message sent from thesource MeNB to the UE does not comprise information instructing the UEto delete a SCG.
 3. The method according to claim 1, further comprising:receiving, by the target MeNB, a configuration response message from theSeNB.
 4. The method according to claim 1, further comprising: sending,by the target MeNB, a configuration completion message to the SeNB,wherein the configuration completion message comprises: an MeNB UE X2APID between the target MeNB and the SeNB allocated by the target MeNB forthe UE, and an SeNB UE X2AP ID, which is allocated by the SeNB.
 5. Themethod according to claim 4, wherein as for a split bearer at the SeNB,the configuration completion message further comprises an evolved radioaccess bearer (E-RAB) ID and a TEID and transmission layer addressallocated by the target MeNB, and wherein in a situation that an SGW isre-selected, as for a SCG bearer, the configuration completion messagefurther comprises a UL TEID and UL transmission layer address allocatedby a new SGW.
 6. The method of claim 1, wherein the ID of the UE at theSeNB comprises a SeNB UE X2 application protocol (X2AP) ID of the UE. 7.A device for inter-master enhanced NodeB (MeNB) handover to a targetMeNB from a source MeNB which provides dual-connectivity together with asecondary eNB (SeNB), the device comprising: a transceiver configured toreceive a handover request message, wherein the handover request messagecomprises an identity (ID) of a user equipment (UE) at the SeNB and aneNB ID of the SeNB; and at least one processor configured to: controlthe transceiver to send to the SeNB a configuration request messageincluding the ID of the UE at the SeNB, control the transceiver to sendto the source MeNB a handover request acknowledge message indicatingthat the SeNB is kept unchanged, and control the transceiver to send apath switch request message to a mobile management entity (MME).
 8. Thedevice of claim 7, wherein the handover request message furthercomprises at least one of: a measurement result of the UE, informationon whether a type of a bearer at the SeNB is a split bearer or a SeNBcell group (SCG) bearer, a cell ID of a secondary cell (Scell) of the UEat the SeNB, a bearer of the UE at the SeNB, a downlink (DL) tunnelendpoint Identifier (TEID) allocated by the SeNB to a split bearer, orDL transmission layer address of an X2 interface allocated by the SeNBto a split bearer.
 9. The device of claim 7, wherein the at least oneprocessor is further configured to control the transceiver to receive aconfiguration response message.
 10. The device of claim 9, wherein theat least one processor is further configured to send a configurationcompletion message to the SeNB, and wherein the configuration completionmessage comprises: an MeNB UE X2AP ID between the target MeNB and theSeNB allocated by the target MeNB for the UE, and an SeNB UE X2AP ID,which is allocated by the SeNB.
 11. The device of claim 7, wherein theID of the UE at the SeNB comprises a SeNB UE X2 application protocol(X2AP) ID of the UE.